1. Field of the Invention
The present invention relates to a liquid ejection head and an image forming apparatus, and more particularly to a liquid ejection head and an image forming apparatus that can simplify liquid flow channels for supplying a liquid to liquid ejection ports, thereby achieving high-speed ejection while supplying liquid efficiently.
2. Description of the Related Art
Conventionally, as an image forming apparatus, an inkjet printer (inkjet recording apparatus) is known, which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (ejection ports) and which records images on a recording medium by ejecting the ink from the nozzles toward the recording medium while causing the inkjet head and the recording medium to move relatively to each other.
In an inkjet printer of this kind, the ink is supplied to pressure chambers from an ink tank via an ink supply channel, and then piezoelectric elements are driven by supplying electrical signals corresponding to the image data to the piezoelectric elements. Therefore, since the diaphragms constituting a portion of each pressure chamber are caused to deform, the volume of the pressure chamber is reduced so as to cause the ink inside the pressure chamber to be ejected from a nozzle in the form of a droplet.
In an inkjet recording printer, one image is formed on a recording medium by combining dots formed by ejecting the ink from the nozzles. In recent years, it has become desirable to form images of high quality on a par with photographic prints, according to inkjet printers. It has been thought that high image quality can be achieved by reducing the size of the ink droplets ejected from the nozzles by reducing the diameter of the nozzles, while also increasing the number of pixels per image by arranging the nozzles at high density.
In order to achieve high density of the nozzles, it is indispensable to devise the composition of the electrical wiring and the ink flow channels suitably. Therefore, conventionally, there have been various proposals for achieving high density of the nozzle arrangement, as well as improving the ink supply efficiency and increasing the printing speed (achieving high-frequency ejection).
For example, it is known that high density of the nozzles can be achieved by providing ink supply channels for supplying ink to the pressure chambers in a diaphragm forming one surface of the pressure chambers, and also forming a common liquid chamber on the rear surface of the diaphragm in such a manner that ink is supplied to the pressure chambers from the common liquid chamber by means of the ink supply channels (see Japanese Patent Application Publication No. 9-226114, for example).
For example, it is also known that the structure of the liquid ejection head can be simplified by providing piezoelectric elements on the surfaces of the pressure chambers opposite to the surfaces on which nozzles are provided; providing a portion of a common liquid chamber for supplying ink on the side adjacent to the piezoelectric elements; and providing a covering on the piezoelectric elements in such a manner that electrodes can be extracted by wire bonding, thin film formation, or the like (see Japanese Patent Application Publication No. 2000-127379, for example).
For example, it is also known that higher density and lower costs can be achieved by disposing piezoelectric actuators on pressure chambers on the nozzle surfaces thereof; adopting a structure in which aluminum plugs pass through laminated layers; and then performing silicon photo-etching to form an inkjet head (see Japanese Patent Application Publication No. 2000-289201, for example).
For example, it is also known that an increased number of nozzles reduced costs and high accuracy can be achieved by providing supply restrictors in a diaphragm; providing an ink supply tank forming an ink supply section on the opposite side of piezoelectric elements from the pressure chambers; forming ink supply ports connecting to the pressure chambers from the ink supply tank and passing through the diaphragm; and causing the ink supply section to act as an insulating sealing cover for the piezoelectric elements and to provide covering and damping functions for the piezoelectric elements (see Japanese Patent Application Publication No. 2001-179973, for example).
For example, it is also known that a porous material having a large number of small internally connected pores, such as a sintered stainless steel member, is used as the ink supply layer so that the ink can pass through the porous material, thereby improving refilling properties, achieving high printing speed and high reliability, and obtaining an inkjet head which has excellent ink preparation characteristics and filtration characteristics for a plurality of types of ink (see Japanese Patent Application Publication No. 2003-512211, for example).
For example, it is also known that interconnection between adjacent pressure chambers can be reduced while suppressing crosstalk by forming a groove formed on the opposite side to the side adjacent to the pressure chamber in at least one position on the surface of a laminated piezoelectric element corresponding to the side wall of a pressure chamber. In this reference, it is described that a nozzle is provided on the side adjacent to the laminated piezoelectric element, and a through hole connecting to the nozzle is provided in the laminated piezoelectric element (see Japanese Patent Application Publication No. 11-138796, for example).
For example, it is also known that high density of nozzles can be achieved by providing a supply channel passing through a diaphragm between two pressure chambers in such a manner that ink is supplied to the respective pressure chambers from a common liquid chamber provided on the upper side of the pressure chamber, while crosstalk (mutual interference) between adjacent nozzles can be prevented by absorbing pressure variations which are caused by reflux from the pressure chambers (see, for instance, Japanese Patent Application Publication No. 11-192699).
As described in Japanese Patent Application Publication Nos. 9-226114, 2000-127379, and 2001-179973, in the case in which a common flow channel (common liquid chamber) or a portion thereof is formed on the opposite side of a piezoelectric body from the diaphragm and the pressure chamber, it is necessary to form a supply channel (supply port) in the diaphragm while disposing only the pressure chamber and the nozzle on the pressure chamber side due to the available space on the pressure chamber side so that the common flow channel passes completely through the diaphragm to the other surface (on the side opposite to the pressure chamber), in order to achieve higher density and a higher ejection driving speed (higher driving frequency). In addition, it is also necessary to install such as the electrical wires for supplying drive signals to the piezoelectric bodies, at high density. However, in this case, since it is required to use a multi-layer flexible cable when the electrical wires are extracted on the same surface as the piezoelectric bodies, then there is a large problem in terms of implementation technology.
In Japanese Patent Application Publication No. 9-226114, it is described that actuators (piezo elements) are arranged at 1440 dpi in one row. In this case, although it is considered to achieve high-density, there is no contemplation of increasing the refilling speed. Therefore, it is difficult to achieve high-frequency driving.
In Japanese Patent Application Publication No. 2000-127379, it is described that a portion of the common liquid chamber (reservoir) is provided on the side adjacent to the piezoelectric elements. However, a portion of the common liquid chamber is naturally situated on the side adjacent to the pressure chambers, and the common liquid chamber is also provided further toward the outer side of the piezoelectric elements than the electrical wiring surface. Therefore, it is not suitable for high density.
In Japanese Patent Application Publication No. 2000-289201, it is described that a piezoelectric actuator is provided on the nozzle side, the IC is unified, and a common liquid chamber is provided on the piezoelectric actuator side (namely, the nozzle side) while electrical wires (aluminum plugs) are formed perpendicularly from the drive circuits. However, the common liquid chamber is formed on the outer side of the piezoelectric actuators, and the aluminum plugs are also formed in positions separate from the piezoelectric actuators and the common liquid chamber so as to pass through the laminated layers. Therefore, since it is required to provide space for forming the plugs, high density is difficult to achieve. In addition, since there is no description relating to the compatibility of IC manufacture and heat treatment or relating to the common liquid chamber, there is no contemplation of increasing the refilling speed.
In Japanese Patent Application Publication No. 2001-179973, it is described that pores for supplying ink are provided in regions in which no piezoelectric elements are situated in a diaphragm made of zirconia. However, since the wiring is situated on the piezoelectric element surface, then it is particularly difficult to adopt a matrix structure to such a shape, and therefore, high density is difficult to achieve.
In Japanese Patent Application Publication No. 2003-512211, it is described that bumps are formed on both faces of insulating positions, and the piezoelectric elements are pressurized by elastic pads so that electrodes are extracted. However, since there is no contemplation of achieving high density, then the connections are also liable to become instable.
In Japanese Patent Application Publication No. 11-138796, it is described that through holes connecting to the nozzles are provided on the side adjacent to the piezoelectric elements. However, there is no description relating to wiring or supply channels, and there is no contemplation of achieving high density or high refilling speed.
In Japanese Patent Application Publication No. 11-192699, it is described that a supply channel is provided in the partition between two pressure chambers. In this case, there is a problem in that the rigidity of the pressure chamber partitions is reduced. In addition, there is no contemplation of achieving high density or high refilling speed.